Fundamental mode coupler



Feb. 27, 1968 J, A HAMMER 3,371,292

FUNDAMENTAL MODE COUPLER Filed Feb. 23, 1965 2 Sheets-Sheet 1 TER MINATI ON MEASURING DEVICE TERMINATION |6 TERMINATION OSCILLATOR FUNDAMENTAL TERMINATION MODE COUPLER FUNDAMENTAL MODE TE HIGHER MODE TEZO HIGHER MODE TE 0| INVENTOR.

Jacobo: A. Hammer ATTORNEYS United States Patent 3,371,292 FUNDAMENTAL MODE COUPLER Jacobus A. Hammer, Clarence, N.Y., assignor to Cornell Aeronautical Laboratory, Inc., Buffalo, N.Y., a corporation of New York Filed Feb. 23, 1965, Ser. No. 434,376 7 Claims. (Cl. 333-) ABSTRACT OF THE DISCLOSURE A fundamental mode coupler including a waveguide having opposite narrow sides and dimensioned so that modes higher than a fundamental mode are possible therein, and exciting waveguides arranged on said opposite narrow sides and providing common walls therewith, these walls being provided with similar coupling holes, whereby only the fundamental mode will be excited in the central waveguide.

This invention relates to a fundamental mode coupler and more particularly to a fundamental mode directional coupler.

It is known to propagate electromagnetic waves through a tubular duct of rectangular cross-section, termed a waveguide. It is also known to provide a coupler by arranging two waveguides side by side to allow electromagnetic Wave action in one waveguide to be transferred or coupled to the other waveguide.

A waveguide up to certain dimensions and proportions, known as a standard waveguide, is capable of transmitting electromagnetic waves having a peak power level in the order of 1 megawatt. To transmitt waves at a higher power level, say about 1000 megawatts which is the power level with which the present invention is concerned, the dimensions of the waveguide must be increased. However, in so doing higher modes as well as the fundamental mode of the wave can be present in the oversize waveguide. This is undesirable. It is preferred to generate only the fundamental mode or substantially so since the higher modes may be considered to represent energy losses.

It is accordingly the primary object of the present invention to generate substantially only the fundamental mode of an electromagnetic wave in a waveguide in which it is possible that modes higher than the fundamental mode can propagate.

This object is achieved in accordance with the inventive concept by providing a fundamental mode coupler including a waveguide having opposite narrow sides and dimensioned so that modes higher than a fundamental mode are possible therein and arranging exciting waveguides on such opposite narrow sides and providing the common walls with similar coupling holes whereby only the fundamental mode will be excited in the central waveguide.

Other objects and advantages of the present invention will be apparent from the following descripition of a preferred embodiment illustrated in the accompanying drawings in which:

FIG. 1 is a perspective schematic view of waveguide apparatus including the fundamental mode coupler of the present invention.

FIG. 2 diagrammatically illustrates the fundamental mode TE of an electromagnetic wave in a waveguide.

FIG. 3 diagrammatically illustrates the higher mode TE of an electromagnetic wave in a'waveguide.

FIG. 4 diagrammatically illustrates the higher mode TE of an electromagnetic wave in a waveguide.

FIG. 5 is a perspective view of the fundamental mode coupler of the present invention as viewed in cross-section.

FIG. 6 is a vertical transverse sectional View thereof.

fFIG. 7 is a fragmentary horizontal sectional view there- 0 FIG. 8 is a fragmentary longitudinal central sectional view thereof taken on line 88 of FIG. 6.

Referring to FIG. 1, the numeral 10 represents generally a device known to those skilled in the art as a hybrid T or magic T which includes three arms in one plane, i.e. opposite side arms 11 and 12 and perpendicular E-arm 13, and also includes a fourth or H-arm 14 in a perpendicular plane. A suitable oscillator or magnetron 15 is shown as associated with arm 14. A suitable termination 16 is shown as associated with arm 13.

Severally connected to the ends of arms 11 and 12 are waveguides 18 and 19, respectively. These waveguides 18 and 19 are identical in size and at their remote ends are associated with suitable identical terminations 20 and 21, respectively.

Intermediate their ends the waveguides 18 and 19 are shown as gradually bent closer to each other and then gradually bent farther apart. Between these juxtaposed portions of the waveguides 18 and 19 is disposed a portion of another waveguide 22. The combination of the adjacent portions of waveguides 18, 19 and 22 provides a fundamental mode coupler represented generally by the numeral 23.

The opposite end portions of waveguide 22 are shown as turned away from the longitudinal extent of coupler 23, terminating at one end in a suitable termination 24 and at its opposite end in a suitable measuring device 25, for example.

Referring to FIG. 5, each of waveguides 18, 19 and 22 is rectangular in cross-section. Central waveguide 22 includes a pair of opposite broad sides 26 and 27 and a pair of opposite narrow sides 28 and 29. As viewed in FIG. 5, waveguide 18 is on the left and waveguide 19 is on the right of waveguide 22. Left waveguide 18 includes a pair of opposite broad sides 38 and 31 and a pair of opposite narrow sides 32 and 33. Right waveguide 19 includes a pair of opposite broad sides 34 and 35 and a pair of opposite narrow sides 36 and 37.

In FIG. 5, broad sides 26, 27, 30, 31, 34 and 35 are shown arranged horizontally and narrow sides .28, 29, 32, 33, 36 and 37 are shown arranged vertically. Sides 28 and 33 for the height of side 33 provide a common wall. Similarly sides 29 and 36 for the height of side 36 provide a common wall.

Outer waveguides 18 and 19 are shown being similarly dimensioned in cross-section but smaller proportionately than intermediate waveguide 22 and centrally and symmetrically arranged on opposite sides thereof.

Each of the common walls 28, 33 and 29, 36 is shown as provided with a series of centrally arranged and longitudinally spaced coupling holes, designated in opposite pairs as 38, 38'; 39, 39', and so on. These holes extend through the corresponding common wall to connect the interiors of the corresponding Waveguides. Thus holes 38 and 39 connect the interiors of waveguides 18 and 22, whereas holes 38' and 39' connect the interiors of waveguides 19 and 22.

Each pair of opposite holes such as 38 and 38' must be similarly shaped, sized and located, although such shape, size and location may be different from an adjacent pair of holes such as 39 and 39'. It is essential that a given pair of opposite holes 38 and 38 be located the same height h above lower broad side 27 of central waveguide 22 as shown in FIG. 6. Preferably, the coupling holes 38, 38, 39, 39', and their fellows not illustrated are circular in shape, identical in diameter, have their horizontal axes midway of the vertical sides 28 and 29, and are spaced at equal intervals longitudinally along the waveguides. However, these coupling holes may have 3 other than a circular shape as shown and also may be spaced longitudinally other than at equal intervals.

While only one pair of opposite holes such as 38 and 38 will provide a coupler, a series of longitudinally spaced holes will provide a directional coupler. The spacing of the coupling holes mainly determines directivity.

It is essential to the invention that the coupling holes are arranged in the narrow sides of the central waveguide 22 but, while the outer or exciting waveguides 18 and 19 are shown as each having one of their narrow sides providing a common wall with the narrow sides of the central Waveguide 22, this is not essential. In any event, outer waveguides 18 and 19 must be dimensioned so that only the fundamental mode is possible therein.

The oscillator in combination with the hybrid T 10 provide means for propagating electromagnetic waves of equal amplitude and phase through the two outer waveguides 18 and 19. Through the pairs of coupling holes such as 38, 3'8 and 39, 39 substantially only the fundamental mode TE (FIG. 2) is excited in central waveguide 22 although dimensionally it is large enough so that higher modes such as TE (FIG. 3) and TE (FIG. 4) could possibly exist therein. It is not desired that such higher modes be established.

Variations may occur to those skilled in the art and hence the embodiment shown is illustrative and not limitative of the present invention which is to be measured by the scope of the appended claims.

What is claimed is:

1. A fundamental mode coupler comprising a first waveguide rectangular in cross-section including a pair of opposite narrow sides and so dimensioned that modes higher than the fundamental mode of an electromagnetic Wave are possible therein, a second waveguide rectangular in cross-section having a side providing a common wall with one of said opposite narrow sides, a third waveguide rectangular in cross-section having a side providing a common wall with the other of said opposite narrow sides, each of said common walls having a coupling hole therethrough connecting the interiors of the corresponding waveguides, such holes being opposite each other and similarly shaped, sized and located, said second and third waveguides being dimensioned so that only the fundamental mode is possible therein, and means for propagating through said second and third waveguides electromagnetic waves having the same amplitude and phase.

2. A fundamental mode coupler comprising a first waveguide rectangular in cross-section including a pair of opposite narrow sides and so dimensioned that modes higher than the fundamental mode of an electromagnetic wave are possible therein, a second waveguide rectangular in cross section having a side providing a common wall with one of said opposite narrow sides, a third waveguide rectangular in cross-section having a side providing a common wall with the other of said opposite narrow sides, said second and third waveguides being similarly dimensioned in cross-section so that only the fundamental mode is possible therein and symmetrically arranged on opposite sides of said first waveguide, each of said common walls having a coupling hole therethrough connecting the interiors of the corresponding waveguides, such holes being opposite each other and similarly shaped, sized and located, and means for propagating through said second and third waveguides electromagnetic waves having the same amplitude and phase.

'3. A fundamental mode coupler comprising a first waveguide rectangular in cross-section including a pair of opposite narrow sides and a pair of opposite broad sides and so dimensioned that modes higher than the fundamental mode of an electromagnetic wave are possible therein, a second Waveguide rectangular in cross-section having a side providing a common wall with one of said opposite narrow sides, a third waveguide rectangular in cross-section having a side providing a common wall and the other of said opposite narrow sides, said second and third waveguides being similarly dimensioned in cross-section so that only the fundamental mode is possible therein and symmetrically arranged on opposite sides of said first waveguide, each of said common walls having a coupling hole therethrough connecting the interiors of the corresponding waveguides, such holes being opposite each other, similarly shaped and sized, and located the same perpendicular distance from one of said broad sides, and means for propagating through said second and third waveguides electromagnetic Waves having the same amplitude and phase.

4. A fundamental mode coupler comprising a first waveguide rectangular in cross-section including a pair of opposite narrow sides and so dimensioned that modes higher than a fundamental mode are possible therein, a second waveguide rectangular in cross-section having a narrow side providing a common wall with one of said opposite narrow sides, a third waveguide rectangular in cross-section having a narrow side providing a common wall with the other of said opposite narrow sides, said second and third waveguides being similarly dimensioned in cross-section but smaller than said first waveguide so that only the fundamental mode can exist therein and symmetrically arranged on opposite sides of said first waveguide, each of said common walls having a coupling hole therethrough connecting the interiors of the corresponding Waveguides, such holes being opposite each other and similarly shaped, sized and located, and means for propagating through said second and third waveguides electromagnetic waves having the same amplitude and phase.

5. A fundamental mode coupler comprising a first waveguide cross-sectionally dimensioned so that modes higher than the fundamental mode of an electromagnetic wave are possible therein, a second waveguide on one narrow side of said first waveguide and having a common wall therewith, a third waveguide on an opposite narrow side of said first waveguide and having a common wall therewith, each of said common walls having a coupling hole therethrough connecting the interiors of the corresponding waveguides, such holes being opposite each other and similarly shaped, sized and located, said second and third waveguides being dimensioned so that only the fundamental mode is possible therein, and means for propagating through said second and third waveguides electromagnetic waves having the same amplitude and phase whereby the fundamental mode of a wave is generated in said first waveguide.

6. A fundamental mode coupler comprising a first waveguide rectangular in cross-section including a pair of opposite narrow sides and so dimensioned that modes higher than the fundamental mode of an electromagnetic wave are possible therein, a second waveguide rectangular in cross-section having a side providing a common wall with one of said opposite narrow sides, a third waveguide rectangular in cross-section having a side providing a common wall with the other of said opposite narrow sides, said second and third waveguides being similarly dimensioned in cross-section so that only the fundamental mode is possible therein and symmetrically arranged on opposite sides of said first waveguide, each of said common walls having a coupling hole therethrough connecting the interiors of the corresponding waveguides, such holes being opposite each other and similarly shaped, sized and located, and means for propagating through said second and third waveguides electromagnetic waves having the same amplitude and phase whereby the fundamental mode of a Wave is generated in said first waveguide.

7. A fundamental mode directional coupler comprising a first elongated waveguide rectangular in cross-section including a pair of opposite narrow sides and so dimensioned that modes higher than a fundamental mode are possible therein, a second elongated waveguide rectangular in cross-section having a side providing a common wall with one of said opposite narrow sides, a third elongated waveguide rectangular in cross-section having a side providing a common wall with the other of said opposite narrow sides, said second and third waveguides being similarly dimensioned in cross-section so that only the fundamental mode is possible therein and symmetrically arranged on opposite sides of said first waveguide, said common walls having a series of pairs of coupling holes extending therethrough to connect the interiors of the corresponding waveguides and longitudinally spaced therealong, said holes in each of said pairs being opposite each other and similarly shaped, sized and located, and means for References Cited UNITED STATES PATENTS 2,748,350 5/1956 Miller 333*10 10 HERMAN KARL SAALBACH, Primary Examiner.

M. NUSS'BAUM, Assistant Examiner. 

